Abstract
The heptapeptide Asn-Gly-Ser-Gln-Met-Arg-Leu, part of a tuberculin-active intracellular mycobacterial protein and having residual tuberculin activity, was synthesized. Biological assays of the synthetic peptide showed it to be recognized as an antigen of mycobacterial origin by its ability to elicit an early allergic reaction in Mycobacterium bovis BCG-infected mice. The synthetic peptide was devoid of any tuberculin activity in BCG-infected mice and in skin tests on M. tuberculosis-sensitized guinea pigs. Purified protein derivative, the complex mixture of proteins of unknown composition which is excreted into the culture medium by M. tuberculosis and is in wide use as a tuberculin-active preparation, was shown to weakly cross-react in radioimmunoassays with the synthetic heptapeptide when 125I-labeled heptapeptide and an anti-heptapeptide antiserum were used.

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